The present invention relates to a door stop, in particular for a door of a motor vehicle, which enables an unhindered movement of a door in a first door opening angular region and for stepless stopping and retaining the door in an arbitrary selected opening position in a second opening angular region.
A known door stop of the above-described type includes a hydraulic cylinder connectable to a door assembly part, a door or a door frame, a stop piston longitudinally displaceable in the hydraulic cylinder and separating two pressure chambers formed in a cavity of the hydraulic cylinder, a piston rod fixedly secured to the stop piston for connecting the stop piston with another part of the door assembly, two separate conduits formed in the stop piston for communicating the two pressure chambers of the cylinder, two closing pistons located in the two separate conduits and displaceable therein in opposite directions between an open position, in which they permit flow of a pressure medium through the conduits from one of the pressure chambers to another of the pressure chambers, and a closing position, in which they block the fluid flow through the conduits, and spring means for biasing the two closing pistons to their closing positions.
In the closing position, the closing pistons keep the door in its selected position until an actuation force is generated in one or the other of the cylinder pressure chambers which exceeds the retaining force of the respective biasing spring. Under the action of such actuation force, one of the closing pistons then moves to its open position, in which it permits flow through the conduit associated therewith, and the door becomes freely pivotable as long as an appropriate actuation force acts on the door.
Such a door stop is disclosed in a German patent No. 1,459,182. The drawback of this known door stop consists in that the beginning of the adjustable door movement must be jerky to bring the closing piston into its open position. This, of course, makes a comfortable door handling, which is required in modern motor vehicles, impossible. Moreover, the known door stop does not permit to achieve a reliable stop of the door immediately after the actuation forces ceases to act on the door, because the biasing force acting on the closing piston cannot be made too large, in view of the requirements to the operation of the door, to overcome the residual pressure medium pressure existing in the flow conduits after the actuation force ceases to act on the door. As a result, the door, after the actuation force ceases to act thereon, still undergoes a creeping movement, which is especially the case with respect to motor vehicle doors, especially when the vehicle stays on an uneven surface, and gravity forces may cause a self-induced movement of the door.
Another door stop is disclosed in a German patent No. 4,239,172. This door stop has a single flow passage controlled by a closing piston, which is spring-biased in its closing direction and is associated with a control conduit with a pressure relief valve for each of the two opposite flow directions. In this door stop, the medium pressure, which is generated in one of the two pressure chambers of the cylinder upon the action of the actuation force on the door, opens a respective pressure relief valve and the closing piston is subjected to the medium pressure and moves against the spring-biasing force into its open position, in which fluid is able to flow through the flow conduit. As soon as the closing piston is moved to its open position, the pressure relief valve of the corresponding control conduit closes, and fluid flows only through the flow conduit.
When the actuation force acting on the door ceases, the same pressure is established in both pressure chambers of the cylinder. As a result, even a weak biasing force moves the closing piston to its closed position. However, this does not insure a reliable fixation of the door in the open position desired by the user. In addition, the manufacturing of such a door stop, because of a need in two pressure relief valves, is rather expensive.
In addition, none of the two above-described door stops provides for a free movement of the door in a sense that first, the door stop provides for movement of the door through a predetermined opening angular region.
Accordingly, an object of the invention is a door stop of the above-described type which would insure application of high retaining forces at the reduced dimensions of the door stop, which would be inexpensive to produce, and which would insure a large as possible comfortable operational handling of the door, with the possibility of a reliable retaining of the door in the selected-by-the-user position.
Another object of the invention is a door stop which would insure the smooth door movement with small actuation forces.